Washing machine and control method thereof

ABSTRACT

Disclosed herein are a washing machine that may effectively remove residual water remaining at the bottom of a tub after completion of washing, and a control method thereof. A drainage motor is driven to remove residual water remaining at the bottom of a tub when a predetermined time elapses after all washing operations are completed. Thereby, the residual water may be prevented from freezing and thus blocking the drain. Further, the residual water may be removed through a control algorithm, without adding a separate device. Thereby, manufacturing costs may be reduced.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Korean Patent Application No. 10-2013-0017196, filed on Feb. 18, 2013 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.

BACKGROUND

1. Field

Embodiments of the present disclosure relate to an electric washing machine to remove residual water from the washing machine and a control method thereof.

2. Description of the Related Art

A washing machine includes a tub to retain water (washing water or rinsing water), a washing tub rotatably installed in the tub to accommodate laundry, a pulsator rotatably installed at the lower portion of the washing tub to form a water current, and a washing motor to generate driving force to rotate the washing tub and the pulsator. The washing machine removes contaminants from laundry using the water current and the surfactant action of the detergent.

The washing machine performs washing through a series operations of removing contaminants from the laundry with water containing dissolved detergent (specifically, washing water), rinsing of removing lather and residual detergent from the laundry with water which does not contain detergent, and removing water from the laundry by rotating the laundry at high speed. After washing is completed through the above operations, there is water which has not been drained, i.e., residual water in the bottom of the tub. When a user removes the laundry from the washing machine, the water remaining in the bottom of the tub gathers around a drainage outlet, which is the lowest portion of the tub.

The drainage outlet may not cause any trouble in those countries in South Asia where the ambient temperature is high. However, in a country having cold winters during which the ambient temperature is low, the drainage outlet may be blocked when the residual water remaining at the drainage outlet freezes. As a result, when the washing machine is used later, water may not be drained and the user may be dissatisfied with the washing machine. Moreover, when the drainage motor is driven by force with the drainage outlet blocked, the motor may be overloaded and break down.

SUMMARY

Therefore, it is an aspect to provide a washing machine that may effectively remove residual water remaining at the bottom of a tub after completion of washing, and a control method thereof.

Additional aspects will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned from practice of the invention.

In accordance with one aspect, a control method of a washing machine including a tub to accommodate water, a drain formed at a bottom of the tub to discharge water, a drainpipe connected to the drain, and a drainage motor installed at the drainpipe to control discharge of the water, includes determining whether a door of the washing machine is opened after completion of a drying operation, counting a door open time of the door when determining that the door is opened, determining whether the counted door open time has reached a first time, and performing a residual water removal operation of removing residual water at the drain by driving the drainage motor when determining that the door open time had reached the first time.

The residual water removal operation may be performed after all operations of the washing machine are completed.

The driving of the draining motor may include continuously driving the drainage motor, or alternatively driving the drainage motor in a non-continuous fashion by turning the drainage motor on/off.

The control method may further include counting time for which the drainage motor is driven, determining whether the counted time has reached a second time, and stopping the drainage motor when determining that the time has reached a second time.

The first time may be set to be longer than the second time. The first time may be at least five minutes, and the second time may be at least three seconds.

In accordance with one aspect, a washing machine includes a tub to accommodate water, a drain formed at a bottom of the tub to discharge water, a drainpipe connected to the drain, a drainage motor installed at the drainpipe to control discharge of the water, a washing tub installed in the tub to accommodate laundry, a door to open and close an inlet for introduction of the laundry, a door switch to detect opening or closing of the door, a controller to count a door open time of the door when determining that the door is opened after completion of a drying operation and to perform a residual water removal operation by driving the drainage motor when determining that the counted door open time has reached a first time.

The controller may perform the residual water removal operation of removing residual water at the drain by driving the drainage motor for a second time.

The controller may count time for which the drainage motor is driven, and when the counted time reaches a second time, may stop the drainage motor to stop performing the residual water removal operation.

The residual water removal operation may be performed after all operations of the washing machine are completed.

In accordance with a aspect, a control method of a washing machine including a tub to accommodate water, a drain formed at a bottom of the tub to discharge water, a drainpipe connected to the drain, and a drainage motor installed at the drainpipe to control discharge of the water, includes determining whether a door of the washing machine is opened, counting a door open time of the door when determining that the door is opened, determining whether the counted door open time has reached a first time, and performing a residual water removal operation of removing residual water at the drain by driving the drainage motor when determining that the door open time reaches the first time, wherein the residual water removal operation is performed after all operations of the washing machine are completed.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:

FIG. 1 is a cross-sectional view showing a configuration of a washing machine according to an exemplary embodiment;

FIG. 2 is a perspective view showing a tub removed from the washing machine of FIG. 1;

FIG. 3 is a control block diagram illustrating the washing machine according to one embodiment;

FIGS. 4A and 4B are flowcharts illustrating a control method of the washing machine according to an embodiment; and

FIGS. 5A and 5B are flowcharts illustrating a control method of a washing machine according to one embodiment.

DETAILED DESCRIPTION

Reference will now be made in detail to the embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout.

FIG. 1 is a cross-sectional view showing a configuration of a washing machine according to an exemplary embodiment.

In FIG. 1, the washing machine 1 includes a cabinet 10 forming an external appearance of the washing machine approximately in the shape of a box, a tub 11 installed in the cabinet 10 to retain water, a washing tub 12 rotatably installed in the tub 11 to retain laundry, and a pulsator 13 rotatably installed in the washing tub 12 to rotate in alternating directions to generate a water current.

The washing tub 12 is formed in the shape of a cylinder having an open top, and is provided with a plurality of drainage holes 12 a on the lateral surface thereof. A balancer 12 b may be mounted to the upper portion of the washing tub 12 to ensure that the washing tub 12 stably rotates at high speed.

Installed at an outer lower portion of the tub 11 are a washing motor 14 to generate driving force to rotate the washing tub 12 and the pulsator 13, and a power conversion device 15 to simultaneously or selectively transfer the driving force generated by the washing motor 14 to the washing tub 12 and the pulsator 13.

A drying shaft 16 having a hollow shape may be coupled to the washing tub 12. A washing shaft 17 installed in a hollow portion of the drying shaft 16 may be coupled to the pulsator 13 via a washing shaft coupling portion 18.

The washing motor 14 is a direct drive (DD) motor having a variable speed function. The washing motor 14 may simultaneously or selectively transfer driving force to the washing tub 12 and/or the pulsator 13 depending on the ascending or descending movement of the power conversion device 15.

Alternatively, a universal motor including a field coil and an armature or, a brushless direct current motor (BLDC motor) including a permanent magnet and an electromagnet may be used as the washing motor 14. Any type of motors may be used so long as such motor is applicable to the washing machine 1. Otherwise, the washing motor 14 may be configured using a belt.

The power conversion device 15 may include an actuator 15 a to generate driving force for power conversion, a rod 15 b to rectilinearly move according to movement of the actuator 15 a, and a clutch 15 c connected to the rod 15 b to turn according to movement of the rod 15 b.

A water level sensor 19 is installed at a lower inner side of the tub 11 to sense the amount of water (water level) in the tub 11.

A drain 20 is formed at the bottom of the tub 11 to discharge water in the tub 11 to the outside, and a first drainpipe 21 is connected to the drain 20. A drainage motor 22 to regulate drainage is installed at the first drainpipe 21, and a second drainage pipe 23 is connected to the outlet of the drainage motor 22 to discharge the water to the outside.

A door 25 to be opened or closed is installed at the upper side of the cabinet 10 to put laundry in the washing tub 12 or remove the laundry from the washing tub 12. A top-cover to be detached or seated depending on opening of the door 25 is installed at the upper side of the cabinet 10.

An inlet 27 is formed in the top cover 26 to enable laundry to be placed in the washing tub 12 or removed from the washing tub 12. The inlet 27 may be opened and closed by the door 25.

Meanwhile, the door 25 is hinged to one side of the top cover 26 to open and close the inlet 27.

In addition, a door switch 30 is installed at one side of the top cover 26 to detect whether the door 25 is opened or closed. The door switch 30 may be installed at any position on the top cover 26 at which the door 25 is seated.

The door switch 30 includes a magnet and a reed switch. The reed switch, which is turned on/off according to contact with the magnet is installed at the top cover 26 at which the door 25 is seated, while the magnet is installed at the leading end of the door 25 contacting the top cover 26. Thereby, opening or closing of the door 25 is detected according to contact between the magnet and the reed switch.

In addition, a water supply pipe 40 to supply water to the tub 11 is installed at an upper portion of the cabinet 10. An external water source is connected to one side of the water supply pipe 40, and the detergent feed unit 41 is connected to the other side of the water supply pipe 40. The water supplied through the water supply pipe 40 is introduced into the tub 11 together with detergent via the detergent feed unit 41. A water supply valve 42 may be installed in the water supply pipe 40 to control supply of water.

The tub 11 may be supported against the cabinet 10 by a suspension 43. Installed between the tub 11 and the cabinet 10 is a check switch 44 that detects shaking of the washing tub 12, which may occur when the user touches the washing tub 12 to take out the laundry. In addition, the check switch 44 may detect excessive vibration of the tub 11 which occurs before the cabinet 10 collides with the tub 11 according to eccentric rotation of the washing tub 12 caused by unbalanced distribution of the laundry.

FIG. 2 is a perspective view showing a tub removed from the washing machine of FIG. 1.

In FIG. 2, the tub 11 is formed in the shape of a cylinder having an open top. A shaft coupling hole 11 a is formed at the center of the tub 11 such that the washing shaft coupling portion 18 of the washing shaft 16 is fitted thereinto.

The bottom surface of the tub 11 is formed in a curved shape to allow water to flow downward. A drain 20 is formed in the bottom surface of the tub 11 to discharge water.

FIG. 3 is a control block diagram illustrating the washing machine according to one embodiment.

In FIG. 3, the washing machine 1 includes an input unit 50, a controller 52, a memory 54, a driving unit 56, and a display unit 58.

The input unit 50, which is manipulated by the user to input commands to perform washing, rinsing and drying by the washing machine 1, may include a key, a button, a switch, a touchpad, and all the other components which generate predetermined input data by being pushed, touched, pressed or turned.

In addition, the input unit 50 includes a plurality of buttons (for power, operation schedule, temperature of washing water, steeping, washing, rinsing, drying, type of detergent, etc.) through which commands related to operation of the washing machine 1 are input by the user. The plurality of buttons includes a course selection button to select one of washing courses according to the type of laundry put into the washing machine 1 (the courses include Standard course, Wool course, and Fine course, and the user may select, for example, the Standard course according to the type of laundry).

The controller 52 is a microcomputer that controls overall operations of the washing machine 1 of washing, rinsing and drying according to operation information input through the input unit 50. In a selected course, the controller 52 sets the frequency of washing and rinsing, a target RPM, an operation factor (On/Off time of the washing motor), and duration of washing and rinsing according to weight (load) of laundry.

In addition, when all operations including supplying water, washing, and drying are completed, the controller 52 detects whether the door 25 is opened through the door switch 30. When the opened state of the door 25 is detected after washing is completed, the controller 52 counts the door open time of the door 25 and determines whether a predetermined time (a proper time of more than about 5 minutes which allows the user to remove the laundry and leave the washing machine, which will hereinafter be referred to as a first time) has passed. When the door open time of the door 25 has passed the first time, it is determined that the user has removed the laundry from the washing machine, and the residual water removal operation is conducted, during which the water remaining at the bottom of the tub 11 is automatically discharged.

The first time may be changed when designing the washing machine 1 according to the specification or capacity of the washing machine 1.

In the residual water removal operation, the drainage motor 22 is driven to discharge the water remaining at the bottom of the tub 11 when the first time has passed after the opened state of the door 25 is detected.

Thereafter, the controller 52 counts the time for which the drainage motor 22 is driven and determines whether a predetermined time (a proper time of more than 3 seconds allowing removal of the water at the bottom of the tub 11, which will hereinafter be referred to as a second time) has elapsed. When the time for which the drainage motor 22 is driven has passed the second time, it is determined that the water remaining at the bottom of the tub 11 has been removed, and driving of the drainage motor 22 is stopped.

The memory 54 may store control data used to control operation of the washing machine 1, reference data used during control of operation of the washing machine 1, operation data created when the washing machine 1 performs a predetermined operation, setting information such as setting data input through the input unit 90 to make the washing machine 1 perform a predetermined operation, the frequency of a specific operation performed by the washing machine 1, user information including the model of the washing machine 1, and malfunction information including causes or positions of the washing machine 1 which malfunctions.

The driving unit 56 drives the washing motor 14, the drainage motor 22 and the water supply valve 42 which are related to operations of the washing machine 1 according to a driving control signal from the controller 52.

The display unit 58 displays the condition of operation of the washing machine 1 and the user manipulation according to a display control signal from the controller 52. When the user tries to operate the washing machine 1 with the door 25 opened or opens the door 25 by force during operation of the washing machine 1, the display unit 58 displays an error message.

Hereinafter, a description will be given of procedures and effects of operation of a washing machine and a control method thereof according to one embodiment.

FIGS. 4A and 4B are flowcharts illustrating a control method of a washing machine according to an embodiment of the present invention.

In FIGS. 4A and 4B, the user opens the door 25 of the washing machine 1, puts laundry into the washing tub 12, and then closed the door 25. When the door 25 is closed, the door 25 is seated at the top cover 26 installed at the upper side of the cabinet 10 to close the inlet 27.

Thereafter, when the user inputs one of washing courses (the courses include, for example, a Standard course, a Wool course, and a Fine course) and operation information related to operation of the washing machine according to the type of laundry, the operation information selected by the user is input to the controller 52 via the input unit 50.

Accordingly, the controller 52 detects weight (load) of laundry put into the washing tub 12 to conduct washing of the laundry (100). The weight of the laundry may be detected in many ways. The weight may be detected by rotating the washing motor 14 at an RPM (for example, about 70 RPM to 150 RPM) for detection of the weight, with a certain duty (90V) applied to the washing motor 14 and obtaining time taken to reach the duty and the angular speed. Alternatively, The weight may be detected by obtaining time taken to reach a predetermined speed (or a predetermined rate of rotation) using an instantaneous acceleration of the washing motor 14. Alternatively, as disclosed in Japanese Patent Application Publication Nos. 2002-336593, 2004-267334, and 1995-90077, the weight of the laundry may be detected by applying torque to the washing motor 14 for a predetermined time, directly or indirectly measuring the moment of inertia of the washing tub 12, and then calculating the weight using the second law of motion (i.e., torque=inertial acceleration).

Alternatively, a load cell may be adopted to detect the weight (load) of the laundry.

When the weight (load) of laundry is detected, the controller 52 sets an RPM and operation factor (on/off time of the motor), a target water level for washing, a target water level for rinsing, duration of washing and rinsing according to the detected weight (load) of laundry.

Setting an RPM and operation factor (on/off time of the motor), a target water level for washing, a target water level for rinsing, duration of washing and rinsing according to the detected weight (load) of laundry is performed in the case that a separate command related to operation of the washing machine 1 is not additionally input by the user. In the case that the user additionally inputs a separate command related to operation of the washing machine 1, the RPM and operation factor (on/off time of the motor), target water level for washing, target water level for rinsing, duration of washing and rinsing are changed according to the command.

Thereafter, the controller 52 operates the water supply valve 42 to supply washing water needed to perform the washing operation.

When the water supply valve 42 is operated, the water supply valve 42 is opened and washing water is supplied to the tub 11 along with detergent via the water supply pipe 40 and the detergent feed unit 41 (102).

Accordingly, the controller 52 detects the level of washing water supplied to the tub 11 through the water level sensor 19 to determine thief the target washing water level has been reached, and continues supply of water until the level of water supplied to the tub 11 reaches the target washing water level.

When the washing water is supplied up to the target washing water level, the controller 52 performs the washing operation by driving the washing motor 14 at the target RPM and operation factor (on/off time of the motor) established for the washing operation, thereby rotating the pulsator 13 leftward and rightward to generate a water current that delivers the detergent containing water (washing water and detergent) to the laundry (104).

When the washing operation is completed within the set washing time, the controller 52 stops the washing motor 14 and drains the detergent containing water (106), and then performs intermediate drying (108).

Subsequently, the controller 52 operates the water supply valve 42 to supply rinsing water needed to perform the rinsing operation.

When the water supply valve 42 is operated, the water supply valve 42 is opened and rinsing water is supplied to the tub 11 via the water supply pipe 40 (110). At this time, the controller 52 controls supply of the rinsing water to supply churning of rinsing water by rotating the pulsator 13 leftward and rightward, in order to improve rinsing performance. Thereby, the laundry stuck to the washing tub 12 due to the intermediate drying performed after the washing operation is separated from the washing tub 12 and well mixed with the water, and therefore rinsing performance may be improved.

Accordingly, the controller 52 detects the level of rinsing water supplied to the tub 11 through the water level sensor 19 to determine whether the water level is the target rinsing water level (the water level determined according to the set amount of rinsing water), and continues supply of water until the level of water supplied to the tub 11 reaches the target rinsing water level.

When the rinsing water is supplied up to the target rinsing water level, the controller 52 performs the rinsing operation by driving the washing motor 14 at the target RPM and operation factor (on/off time of the motor) established for the rinsing operation, thereby rotating the pulsator 13 leftward and rightward to generate a water current that causes the rinsing water to contact the laundry (112).

When the rinsing operation is completed within the set rinsing time, the controller 52 stops the washing motor 14 and discharges the rinsing water (114). Such rinsing operation is repeated a determined number of times.

When the rinsing operation is repeated a determined number of times and the last rinsing is completed, the controller 52 determines whether the drying operation should be performed (116).

When it is determined that the subsequent operation is not the drying operation in Operation 116, the controller 52 performs the intermediate drying (118), and then goes back to Operation 110 and performs subsequent operations.

When it is determined that the subsequent operation is the drying operation in Operation 116, the controller 52 performs the drying operation at the RPM set for final drying (about 700 RPM to about 1000 RPM) (120).

At this time, the controller 52 drives the drainage motor 22 through the driving unit 56. Thereby, the water in the tub 11 is discharged to the outside via the first and second drainpipes 21 and 23.

When the drying operation is completed, the controller 52 stops driving the washing motor 14 and the drainage motor 22 through the driving unit 56, and terminates all the operations of the washing machine 1.

When all the operations are terminated, the user can open the door 25 and remove the laundry.

Accordingly, when the drying operation is completed and thus all the operations of the washing machine 1 are terminated, the controller 52 detects whether the door 25 is opened. To this end, whether the door 25 is opened is detected using the door switch 30 installed at one side of the top cover 26.

When the user opens the door 25, the magnet installed at the leading end of the door 25 contacting the top cover 26 is separated from the reed switch installed at the top cover 26 and thus opening of the door 25 may be detected.

Thereby, the controller 52 determines whether the door 25 is opened using the door switch 30 (122). In the case that the door 25 is not opened, the controller 52 waits for the residual water removal operation until the door 25 is opened.

When it is determined that the door 25 is opened in operation 122, the controller 52 counts the door open time of the door 25 (124), and determines whether the counted door open time has reached the determined first time (of more than about 5 minutes) (126).

When it is determined that the first time has not elapsed in operation 126, the controller 52 returns to operation 124 and performs subsequent operations.

When it is determined that the first time has elapsed in operation 126, the controller 52 drives the drainage motor 22 through the driving unit 56 (128).

When removing the laundry, the user touches the washing tub 12. Thereby, the washing tub 12 is shaken. The shaken washing tub 12 hits the tub 11, causing the water remaining at the bottom of the tub 11 to gather at the drain 20, which is the lowest portion of the tub 11.

Therefore, when the drainage motor 22 is driven, the residual water that has moved to the drain 20 from around the bottom of the tub 11 after completion of washing is discharged to the outside through the first and second drainpipes 21 and 23.

Thereafter, the controller 52 counts the time for which the drainage motor 22 is driven, and determines whether the determined second time (of more than about 3 seconds) has elapsed (130).

When it is determined that the second time has not elapsed in operation 130, the controller 52 goes back to operation 128 and performs subsequent operations.

When it is determined that the second time has elapsed in operation 130, the controller 52 stops driving the drainage motor 22 through the driving unit 56 and terminates the residual water removal operation (132).

Hereinafter, a description will be given of an operation of detecting shaking of the washing tub 12 which occurs when the door 25 is opened or the user touches the washing tub 12 to remove the laundry to detect completion of all the operations of the washing machine 1 and discharge the residual water gathering near the drain 20, with reference to FIGS. 5A and 5B.

FIGS. 5A and 5B are flowcharts illustrating a control method of a washing machine according to one embodiment. A description of the same parts as those shown in 4A and 4B will be omitted.

Referring to FIGS. 5A and 5B, the user opens the door 25 of the washing machine 1, puts the laundry into the washing tub 12, and then closes the door 25.

Thereafter, when the user inputs a washing course according to the type of the laundry and operation information related to operation of the washing machine, the controller 52 detects the weight (load) of the laundry in the washing tub 12 to perform the washing operation (200).

When the weight (load) of laundry is detected, the controller 52 operates the water supply valve 42 to supply washing water needed to perform the washing operation.

When the water supply valve 42 is operated, the water supply valve 42 is opened and washing water is supplied to the tub 11 along with detergent via the water supply pipe 40 and the detergent feed unit 41 (202).

When the washing water is supplied up to the target washing water level, the controller 52 performs the washing operation by driving the washing motor 14 at the target RPM and operation factor (on/off time of the motor) established for the washing operation, thereby rotating the pulsator 13 leftward and rightward to generate a water current that delivers the detergent containing water (washing water +detergent) to the laundry (204).

When the washing operation is completed in the set washing time, the controller 52 stops the washing motor 14 and drains the detergent containing water (washing water +detergent) (206), and then performs intermediate drying (208).

Subsequently, the controller 52 operates the water supply valve 42 to supply rinsing water needed to perform the rinsing operation.

When the water supply valve 42 is operated, the water supply valve 42 is opened and rinsing water is supplied to the tub 11 via the water supply pipe 40 (210).

When the rinsing water is supplied up to the target rinsing water level, the controller 52 performs the rinsing operation by driving the washing motor 14 at the target RPM and operation factor (on/off time of the motor) established for the rinsing operation, thereby rotating the pulsator 13 leftward and rightward to generate a water current that causes the rinsing water to contact the laundry (212).

When the rinsing operation is completed within the set rinsing time, the controller 52 stops the washing motor 14 and discharges the rinsing water (214). Such rinsing operation is repeated a predetermined number of times.

When the rinsing operation is repeated the determined number of times and the last rinsing is completed, the controller 52 determines whether the subsequent operation is the drying operation (216).

When it is determined that the subsequent operation is not the drying operation in operation 216, the controller 52 performs the intermediate drying (218), and then returns to operation 210 and performs subsequent operations.

When it is determined that the subsequent operation is the drying operation in operation 216, the controller 52 performs the drying operation at the RPM set for final drying (about 700 RPM to about 1000 RPM) (220).

At this time, the controller 52 drives the drainage motor 22 through the driving unit 56. Thereby, the water in the tub 11 is discharged to the outside via the first and second drainpipes 21 and 23.

When the drying operation is completed, the controller 52 stops driving the washing motor 14 and the drainage motor 22 through the driving unit 56, and terminates all the operations of the washing machine 1.

When all the operations are terminated, the user may open the door 25 and remove the laundry.

Accordingly, when the drying operation of the controller 52 is completed and thus all the operations of the washing machine 1 are terminated, it is determined whether the door 25 is opened (222). In the case that the door 25 is not opened, the controller 52 waits for the residual water removal operation until the door 25 is opened.

When it is determined that the door 25 is opened in Operation 222, the controller 52 counts the door open time of the door 25 (224).

When the user touches the washing tub 12 while removing the laundry, the washing tub 12 is shaken. The shaken washing tub 12 hits the tub 11, thereby hitting the check switch 44 installed between the tub 11 and the cabinet 10.

When the drying operation is completed and thus all the operations of the washing machine 1 are terminated, the controller 52 determines whether the check switch 44 is turned on with the door 25 in the opened state (226). In the case that the check switch 44 is not turned on, the controller 52 waits for the residual water removal operation.

When it is determined that the check switch 44 is turned on in operation 226, the controller 52 determines whether the counted door open time of the door 25 reaches the determined first time (of more than about 5 minutes) (228).

When it is determined that the first time has not elapsed in operation 228, the controller 52 returns to operation 224 and performs subsequent operations.

When it is determined that the first time has elapsed in Operation 228, the controller 52 drives the drainage motor 22 through the driving unit 56 (230).

When the user touches the washing tub 12 during removal of the laundry, the washing tub 12 is caused to shake and hits the tub 11. Accordingly, the water remaining at the bottom of the tub 11 gathers at the drain 20, which is the lowest portion of the tub 11.

Therefore, when the drainage motor 22 is driven, the residual water that has moved to the drain 20 from around the bottom of the tub 11 after completion of washing is discharged to the outside through the first and second drainpipes 21 and 23.

Thereafter, the controller 52 counts the time for which the drainage motor 22 is driven, and determines whether the determined second time (of more than about 3 seconds) has elapsed (232).

When it is determined that the second time has not elapsed in operation 232, the controller 52 returns to operation 230 and performs subsequent operations.

When it is determined that the second time has elapsed in operation 232, the controller 52 stops driving the drainage motor 22 through the driving unit 56 and terminates the residual water removal operation (234).

In the illustrated embodiment, an algorithm for removing the residual water remaining at the bottom of the tub 11 by continuously driving the drainage motor 22 for the second time when all the operations are completed and the first time has passes is described as an example. However, embodiments are not limited thereto. The object and effect described above may be achieved by intermittently driving the drainage motor 22 for the second time.

Alternatively, the residual water remaining at the bottom of the tub 11 may be removed by driving the drainage motor 22 for a time shorter or longer than the second time.

As is apparent from the above description, according to the proposed washing machine and control method thereof, a drainage motor is driven to remove residual water remaining at the bottom of a tub when a predetermined time elapses after all washing operations are completed. Thereby, the residual water may be prevented from freezing and thus blocking the drain. Further, the residual water may be removed through a control algorithm, without adding a separate device. Thereby, manufacturing costs may be reduced.

Although a few embodiments have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents. 

What is claimed is:
 1. A control method of a washing machine including a tub to accommodate water, a drain formed at a bottom of the tub to discharge water, a drainpipe connected to the drain, and a drainage motor installed at the drainpipe to control discharge of the water, the control method comprising: determining whether a door of the washing machine is opened after completion of a drying operation; counting a door open time of the door when determining that the door is opened; determining whether the counted door open time has reached a first time; and performing a residual water removal operation of removing residual water at the drain by driving the drainage motor when determining that the door open time has reached the first time.
 2. The control method according to claim 1, wherein the residual water removal operation is performed after all operations of the washing machine are completed.
 3. The control method according to claim 1, wherein the driving of the draining motor comprises: continuously driving the drainage motor.
 4. The control method according to claim 1, further comprising: counting time for which the drainage motor is driven; determining whether the counted time has reached a second time; and stopping the drainage motor when determining that the time has reached a second time.
 5. The control method according to claim 4, wherein the first time is set to be longer than the second time.
 6. The control method according to claim 5, wherein the first time is at least five minutes.
 7. The control method according to claim 5, wherein the second time is at least three seconds.
 8. A washing machine comprising: a tub to accommodate water; a drain formed at a bottom of the tub to discharge water; a drainpipe connected to the drain; a drainage motor installed at the drainpipe to control discharge of the water; a washing tub installed in the tub to accommodate laundry; a door to open and close an inlet for introduction of the laundry; a door switch to detect opening or closing of the door; a controller to count a door open time of the door when determining that the door is opened after completion of a drying operation and to perform a residual water removal operation by driving the drainage motor when determining that the counted door open time has reached a first time.
 9. The washing machine according to claim 8, wherein the controller performs the residual water removal operation of removing residual water at the drain by driving the drainage motor for a second time.
 10. The washing machine according to claim 8, wherein the controller counts time for which the drainage motor is driven, and when the counted time reaches a second time, stops the drainage motor to stop performing the residual water removal operation.
 11. The washing machine according to claim 8, wherein the residual water removal operation is performed after all operations of the washing machine are completed.
 12. A control method of a washing machine including a tub to accommodate water, a drain formed at a bottom of the tub to discharge water, a drainpipe connected to the drain, and a drainage motor installed at the drainpipe to control discharge of the water, the control method comprising: determining whether a door of the washing machine is opened; counting a door open time of the door when determining that the door is opened; determining whether the counted door open time has reached a first time; and performing a residual water removal operation of removing residual water at the drain by driving the drainage motor when determining that the door open time has reached the first time, wherein the residual water removal operation is performed after all operations of the washing machine are completed.
 13. The control method according to claim 1, wherein the driving of the draining motor comprises: driving the drainage motor by turning the drainage motor on/off.
 14. A washing machine comprising: a tub to accommodate water; a drain formed at a bottom of the tub to discharge water; a drainpipe connected to the drain; a drainage motor installed at the drainpipe to control discharge of the water; a washing tub installed in the tub to accommodate laundry; a door to open and close an inlet for introduction of the laundry; a door switch to detect opening or closing of the door; a check switched to detected if the wash tub has been moved while the door is opened; a controller determines if the check switch is turned on while the door is open and to count a door open time of the door when determining that the door is opened after the check switch is turn on, to perform a residual water removal operation by driving the drainage motor when determining that the counted door open time has reached a first time. 